The present invention may be considered an improvement over my earlier U.S. Pat. No. 4,107,127. The invention described there related to resins and glass-fiber-reinforced ducts and other articles made therefrom. The resins were products made from resorcinol and formaldehyde, and in some instances incorporating phenol.
There are advantages to using resins that have a higher percentage of solids than was present in my earlier invention. Typically, in U.S. Pat. No. 4,107,127 the resin had about 42% solids; the non-volatiles could be raised up to slightly over 64% solids, but not beyond that.
There are advantages, however, in having solids contents from the mid-60%'s to the lower 80%'s. The problem with having such higher solids content has been that such resins tended to be too viscous, and their application to the fibers became difficult or inconsistent. Particularly, when working with such fibrous materials as glass fibers and glass fiber cloth, the glass did not tend to wet out properly when high-solids-content resins were used. It is generally not desirable to obtain higher solids content simply by adding fillers, but whether the resin itself has high solids content or fillers are added, the problem is there is too high a viscosity for the product to be of practical use.
In the earlier patent and in products made in further developing the patented invention, higher solids content was achieved by reacting the components to produce a polymeric syrup having around 64%-83% non-volatiles or solids. However the viscosity of such a syrup was about 1,000 to 3,000 centipoises. These high viscosities made it difficult to use the resultant resin for wetting out or saturating glass fiber materials, especially when paraformaldehyde (the then preferred aldehyde), was used alone as the source of the additional formaldehyde needed for room temperature cure. This problem occurred particularly in the use of filament winding roving, where a resin bath container was filled with the resin mixture and glass strands were drawn through the resin mix to wet each strand with the resin. The strands were then drawn onto a rotating mandrel or tool which might be of various shapes, including round, square, and rectangular. The viscosity of the liquid and the velocity of the strands through the resin mix created a back pressure or pull on the glass strands which tended to be so large that it exceeded the tensile strength of the strands, and the strands broke. Thus, it became difficult, if not impossible, to create a finished product from such strands. When fillers of various sorts were added to resin mixes to provide even higher solids content, in order to compensate for the shrinkage of the resin mix as the volatiles evaporated, those fillers compounded the difficulties by further increasing the viscosity of the resin mix.
Thus, it is an object of the present invention to provide a fiber-and-resin material and articles made therefrom which have high solids content but also have workable viscosities at the time of manufacture and, in addition, impart to the finished material high flame resistance and low smoke evolution.
Another object of the invention is to provide a method which enables practical application of these high solids content, fire-resistant materials.
Another object of the invention is to provide a way of reducing the viscosity of the fire-resistant resins during manufacture of fiber-reinforced sheets and shapes without unduly lowering the solids content, so that desirable products can be produced.